import math


def gcd(a, b):
    if b == 0:
        return a
    else:
        return gcd(b, a % b)


class Fraction:
    def __init__(self, up=0, down=1):
        if up * down < 0:
            up = -math.fabs(up)
            down = math.fabs(down)
        else:
            up = math.fabs(up)
            down = math.fabs(down)
        self.up = up
        self.down = down
        self.rationalize()

    def __str__(self):
        return '%d/%d' % (self.up, self.down)

    def __add__(self, other):
        return Fraction(self.up * other.down + other.up * self.down, self.down * other.down)

    def rationalize(self):
        g = gcd(self.up, self.down)
        self.up /= g
        self.down /= g


s = Fraction()
for i in range(1, 20 + 1):
    if i % 2 == 0:
        s = s + Fraction(1, i)
    else:
        s = s + Fraction(1, -i)
print(s)
